Police believe the photos were snapped by the boy's mother, Elizabeth Johnson, on the last day little Gabriel was seen alive.

Tempe police Lt. Mike Horn appeared on CBS News' "The Early Show" Tuesday, saying the pictures are causing "great concern" to investigators and are raising questions about the mother's treatment of Gabriel.

Elizabeth Johnson, 23, has stymied police efforts to find her child. She was arrested Dec. 30 after a two week road trip that took her to San Antonio and eventually Miami. When police picked her up, her baby was gone.

The boy's biological father, Logan McQueary, says she texted him that she had killed Gabriel and later told him that she put Gabriel's body in a diaper bag and threw it in a trash bin.

But Elizabeth Johnson also told CBS affiliate KPHO, in a phone interview, that she gave Gabriel to a couple she didn't know at a San Antonio park, and that she only said she killed the boy to get back at McQueary.

Elizabeth Johnson has been indicted on charges of kidnapping, child abuse and custodial interference. She remains in custody.

Despite the alarming new photos, Horn says police remain "optimistic" that Gabriel is still alive. They've had "indications" that there may have been a plan to give the boy up for adoption, he said, but also acknowledged that things aren't looking good.

"Unfortunately, as each day passes, we also have to wrestle with the fact that Elizabeth may have carried out what she originally said, and that she killed him," Horn told "The Early Show".